1. Technical Field
The present invention relates to a converting controller, and more particularly to a converting controller with a protection output pin.
2. Description of Related Art
FIG. 1 is a schematic diagram of a QX9910 controller applied on an LED driving circuit, which the QX9910 controller is produced by QX Micro Devices Co., Ltd. The LED driving circuit, which comprises a converting circuit and a QX9910 controller 10, is used to drive an LED module 20. The converting circuit comprises an inductance L, a schottky diode Z, a switch SW and a current detecting resistance R. The QX9910 controller 10 controls the turn-on and turn-off states of the switch SW, and thereby input electric power of an input power source Vin is inputted into the converting circuit and is converted into an appropriate power source to drive the LED module 20 for emitting light. Besides, an input driving circuit can be added, which comprises an input resistance Rin, an input capacitance Cin and an input zener diode Zin. The input driving circuit is coupled with the input power source Vin to generate a power source VDD that supplies the power demanded by the QX9910 controller 10 via a power pin VD. An enabling pin EN of the QX9910 controller 10 is also coupled with the power pin VD, and the QX9910 controller 10 starts to perform operation when the power source VDD reaches an activation level.
The QX9910 controller 10 comprises a detecting resistance Rcs, a detecting capacitance Ccs, a comparator 2, a SR flip-flop 4, a driving circuit 6, a constant off-time circuit OFT and a reference voltage generator BG. The current detecting resistance R detects the current flowing though the LED module 20 to generate a current detecting signal Ifb when the switch SW is turned on. The detecting resistance Rcs and the detecting capacitance Ccs are coupled with the current detecting resistance R via the detecting pin CS to filter the current detecting signal Ifb which is inputted into a non-inverting terminal of the comparator 2. An inverting terminal of the comparator 2 receives a reference level 250 mV generated by the reference voltage generator BG, and generates a high-level output signal when the level of the current detecting signal Ifb is higher than 250 mV. A set terminal S of the SR flip-flop 4 is coupled with the constant off-time circuit OFT, and a reset terminal R thereof is coupled with an output terminal of the comparator 2, and an output terminal Q is coupled with the driving circuit 6. The driving circuit 6 is coupled with the constant off-time circuit OFT, and is also coupled with a controlled terminal of the switch SW via a driving pin DR. The SR flip-flop 4 turns off the switch SW via the driving circuit 6 when the reset terminal R receives the high-level output signal from the comparator 2. At this time, the constant off-time circuit OFT starts to count time. The constant off-time circuit OFT triggers the SR flip-flop 4 to turn on the switch SW again when an off period of the switch SW reaches a preset off period. The preset off period of the constant off-time circuit OFT is determined by a RC circuit which is composed of a set resistance Rf and a set capacitance Cf and is coupled with an off period set terminal TOF.
However, the QX9910 controller 10 has no mechanism to protect the circuit from abnormal operations. When at some situations of requiring other circuit(s) to perform protecting function(s), the QX9910 controller 10 also needs to increase additional pin(s) to communicate with the other circuit(s), thus increasing the package cost thereof.